In recent years, performance of mobile phones has been greatly improved and new standards have been established one after another.
For example, in order to meet a next generation LTE (Long Term Evolution) standard, it is indispensable to widen the bandwidth of an amplitude modulator. However, if a conventional technology is employed to design an amplitude modulator having a widened bandwidth, an operational amplifier having a very wide bandwidth characteristic is needed. Accordingly, an increase in power consumption and an increase in a chip area cannot be avoided, and moreover, phase compensation for preventing oscillation becomes difficult.
On the other hand, with respect to a mobile phone, there is a very strong demand for a longer-life battery, reduction in size and weight, and low costs. Therefore, an increase in power consumption and an increase in a chip area are not desirable.
Conventional amplitude modulators are described in detail in Non-Patent Literatures 1 to 3.
Since conventional amplitude modulators are mostly configured by analog circuits, reduced power consumption as a result of miniaturization of CMOS and reduction of a chip area cannot be expected, unlike in a digital circuit. Moreover, since there is a wide variation in DC offsets, group delays, and the like due to property variations among components, a separate circuit for compensating them is necessary to improve performance.